The Relation Between GABA and L-Arginine Levels With Some Stroke Risk Factors in Acute Ischemic Stroke Patients

Changes in extra and intracellular neurotransmitter amino acids concentration in the early stage of acute cerebral ischemia have been reported. In this the study, serum level of gamma aminobutyric acid (GABA) and L-Arginine in acute ischemic stroke patients was assessed. 60 patients with acute ischemic stroke and sixthy healthy volunteers as a control group were assessed. Serum GABA was measured with modified enzymatic method and serum L- Arginine was measured by modified Sakaguchi method. Serum GABA level in stroke cases was lower than that of the control group. There was no relationship between GABA level and age or gender. Also, no significant correlation was observed between GABA levels with ischemic stroke risk factors such as smoking, diabetes mellitus, and hypertension. Serum L- Arginine level in patients was slightly increased in comparison with control group. There was a positive relationship between serum L- Arginine level and acute ischemic stroke risk factors. Serum GABA level was reduced in patients and had no correlation with acute ischemic stroke risk factors.

revious studies demonstrated that in mammalian central nervous system, gamma aminobutyric acid (GABA) is a major inhibitory neurotransmitter (1). In the brain, GABA binds to receptors that cause hyperpolarization in neurons.
There are two classes of GABA receptors: GABA a receptor, is a part of ligand-gated ion channel complex and GABA b receptors, metabotropic receptors which are G protein coupled receptors (2).
It has been reported that GABA's major role is to reduce neural excitability in human. It also regulates muscle tone (3). The implication of excitotoxicity and the glutamate-calcium cascade in the development of neural injury after brain ischemia were proven previously (4)(5)(6)(7). Some experimental evidence suggests that after ischemic stroke, glutamate efflux increases in brain and causes intracellular Ca2+ increase, resulting in neuronal injury. Ischemic stroke also triggers cytotoxic cascades leading to expression of cell death (7). GABA as an inhibitory neurotransmitter can counteract glutamate effect and reduces neural injury. Correspondingly, there is increasing interest in studies of excitatory and inhibitory neurotransmitter levels in body fluid of acute ischemic stroke patients (8). Some studies assessed the level of excitatory and inhibitory neurotransmitters in cerebrospinal fluid (9,10), extracellular fluid (11) and plasma (12)(13)(14).
L-Arginine is an amino-acid that has an important role in cell division, immune function and release of hormones. It is synthesized from citrullin by two cytosolic enzymes argininosuccinate synthetize (ASS) and argininosuccinate lyase (ASL). Some data have revealed that L-Arginine is a precursor of nitric oxide (NO). NO has both neurotoxic and neuroprotective roles. In this regard, NO generation has been related to brain damage in acute ischemic stroke (15). Researchers reported that GABA receptor agonists had neuroprotectant effect in reducing infarct size (12) and after stroke, the patients had lower GABA levels. These results suggest that the function of GABA is decreased outside the infarct. Therefore, further researches are needed for elucidation of the possible role of GABA changes in stroke. In this study, we evaluated serum GABA and L-arginine levels in acute stroke patients and their relationship with acute ischemic stroke risk factors.

GABA assay
Serum GABA was measured by modified enzymatic method previously described (16).

Statistical analyses
Results for the subject group followed a normal distribution, we used parametric methods, two independent test, and Mann-Whitney U test to compare the groups. Also, Spearman correlation test was used to evaluate the correlation values.
Results are expressed as mean±SD, and p<0.05 was considered as statistically significant and subject groups were compared using one-way analysis of variance.

Results
In the present study the mean age of the patients was 64 years (SD=7.2) and 23 of the subjects were females. Clinical characteristics of patients and control group was shown in Table 1.

Discussion
One important finding in the current study is that, as compared with normal subjects, serum GABA level decreased in acute ischemic stroke patient group. Furthermore, it is clear that due to decrease of GABA level, various anxiety disorders are triggered, because GABA plays an important role in overall brain function. In this regard, researchers reported that the use of GABA receptor agonist for the treatment of patients with acute ischemic or hemorrhagic stroke is not suitable (12).
In another study, researchers reported that preischemic treadmill training decreased glutamate  release and increased GABA release during the acute phase of cerebral ischemia/reperfusion (13). It is well known that GABA plays an important role in modulating brain repair (14). After ischemia, a reduction in GABA-ergic neuronal activity, an increase in neuronal or glial GABA uptake was reported (18,19). In addition, the regulation of the activity of dopaminergic system is under the influence of GABA ergic and glutaminergic system (20).
We hypothesized that the reduction of serum The present study had some limitations such as being a single center study. Also, the number of studied subjects was relatively low.
In conclusion, serum GABA levels were reduced in acute ischemic stroke patients and had no correlation with acute ischemic stroke risk factors. However, serum L-Arginine levels were slightly increased in acute ischemic stroke patients.
In addition, it has a positive correlation with acute ischemic stroke risk factors.

Acknowledgments
Financial support was received from the medicine faculty of Babol university of medical sciences (Research proposal number 1695 and thesis number 44).